The invention relates to an apparatus for pelletizing strands of polymer emerging in molten form from dies with a pelletizer, in which apparatus a cooling section carrying a coolant flow and a dewatering section are provided between the dies and the pelletizer.
An apparatus of this type is known from DE-A 197 28 661. In the case of this apparatus, as in the case of other apparatuses of a similar type of design, there is the problem of reliably guiding the strands at the end of the dewatering section to an inlet of the pelletizer, in particular if a circulating conveyor belt is provided in the dewatering section. This problem is particularly marked if materials remaining soft even in the final state of the strands are involved. If the strands are transported here just on the basis of a pushing action, the strands tend to meander, which leads to unevenly cut pellets.
The invention is based on the object of improving the guidance of the strands in the region referred to. This takes place according to the invention by a running-in rest being arranged upstream of the pelletizer, adjoining the dewatering section and provided with at least one air-nozzle arrangement, which is arranged transversely to the running direction of the strands, is designed as a step in the running-in rest and is intended for generating a stream of air directed essentially parallel to the running direction of the strands, which takes with it the strands supplied to the running-in rest.
The air-nozzle arrangement designed as a step in the region of the running-in rest inevitably produces an air flow which runs parallel to the running-in rest downstream of the step, so that the strands arriving at this region over the step are transported continuously and only in the direction of the running-in rest and are therefore taken along by the stream of air, so that the strands do not spend any particular time on the running-in rest and the strands are therefore fed to the pelletizer uniformly as they are delivered by the dewatering section. In this case, the step in the running-in rest is the major factor for the design of the air-nozzle arrangement, since on the one hand the step causes only a slight deflection of the strands from their straight alignment and on the other hand the step offers a favorable starting direction for the air-nozzle arrangement, since the stream of air supplied by the air-nozzle arrangement emerges virtually perpendicularly from the step and then, as it proceeds, follows the running-in rest.
The air-nozzle arrangement in the step may expediently be designed as a slot nozzle. This then extends transversely over the width of the running-in rest. It is also possible, however, to design the air-nozzle arrangement as a row of individual nozzles arranged next to one another in the step, which is favorable for the formation of the step for technical production-related reasons. In addition, the choice of a favorable diameter of the nozzles provides a particularly high flow rate for the stream of air.
In order to increase the effect on the strands carried by the running-in rest, further air nozzles directed in the running direction of the strands may be provided above the running-in rest.
The running-in rest may be designed in such a way that it can be removed from between the dewatering section and the pelletizer. In this case, removal of the running-in rest creates a free space between the dewatering section and the pelletizer and consequently provides particularly good accessibility to the pelletizer, which is of advantage in particular in the case of repairs or cleaning of the pelletizer.
The removal of the running-in rest may take different forms. For instance, it is possible to arrange the running-in rest in such a way that it can be swung out. The running-in rest may, however, also be designed in such a way that it can be pushed out.